//abb
import java.util.Scanner;

注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
   public static void main(String[] args) {
       Scanner in = new Scanner(System.in);
        注意 hasNext 和 hasNextLine 的区别
       while (in.hasNextInt()) {  注意 while 处理多个 case
           int n = in.nextInt();
           char[] arr = in.next().toCharArray();
           int len = arr.length;
           long[] dp = new long[len];
           long[] hash1 = new long[27];
           long[] hash2 = new long[26];
           for (int i = 0; i  len; i++) {
               if (i  1) {
                   dp[i] = hash2[arr[i]-'a'];
               }
               hash1[arr[i]-'a']++;
               hash1[26]++;
               hash2[arr[i]-'a'] += hash1[26]-hash1[arr[i]-'a'];
           }
           long sum = 0;
           for (int i = 0; i  len; i++) {
               sum += dp[i];
           }
           System.out.println(sum);
       }
   }
}